Easily processed polymeric compounds and method of making same



Patented Sept. 9, 1952 OFFICE EASILY PROCESSED POLYMERIC COM- POUNDS AND METHOD OF MAKING i SAME Theodore A. Te Grotenhuis, Olmsted Falls, Ohio N 6 Drawing.

This application is a continuation-impart of my prior application, Serial No. 559,848, ,filed October 21, 1944, now Patent No. 2,457,097, and the invention relates to a synthetic rubberlike compound and to a method of making same. It particularly relates to vulcanizable synthetic rubberlike compounds that are easily processible and extrudable, and retain their extruded shape, and to a method of preparing such compounds.

The synthetic rubbers, particularly those of the Buna-type, which are'polymers or copolymers of a conjugated diolefinic compound, such as butadiene or copolymers of such diolefinic compounds with one or more mono-olefines copolymerizable therewith, are generally characterized by having relatively low tensile strength and very poor properties unless they are compounded with. a reinforcing filler, such as carbon black and the like. These Buna-type synthetics thus differ greatly from natural rubber, which has a very high gum strength and does not require any reinforcing filler.

A filling material, when sufficiently fine, greatly increases the strength of most of the synthetic rubbery polymers; but such filling material also has the effect of greatly increasing the stiffness and hardness of the compound, rendering it-less rubberlike. Frequently it is desired to prepare relatively soft flexible articles similar to gum rubbers from synthetic rubbers, and the incorporation of pigments, such as carbon black and the like, is impossible because of the resultant hardness they contribute to the rubber compound.

It is one object of the present invention to prepare a compound suitable for producing synthetic rubber articles of low pigment loading and having properties in a gum rubberlike state superior to those generally prepared from homogeneous rubber compounds.

One of the most economical methods of forming rubbery materials is by extrusion processes wherein the material is extruded under high pressure through an orifice of the desired shape. In the extrusion of rubbery materials one of the great difiiculties is due to the fact that rubbery materials have a very substantial tendency to change in shape after they are emitted from the extrusion die. This is either due to the elastic memory in the plastic material and a tendency to retain the shape it held before it was extruded, or due to the extreme softness of the material and a tendency to flow during the curing operation. To prevent the elastic memory from effecting change of shape afterextrusion, it has been the general practice in the industry to plasticize Application December 17, 1948, Serial No. 65,968

8 Claims. (01. zen-29.7)

2 V the rubbery materials prior to extrusion to such an extent that little, if any, elastic memory is retained. This, however, increases their tendency for plastic flow after extrusion. To reduce this latter, a substantial amount of fillers, such as pigments, carbon black and the like, has been considered necessary.

The plasticization'of the rubber so that it can be extruded is recognized as being greatly detrimental to the strength of the extruded article, probably because the molecular structure of the polymer is radically changed by the plasticization or mastication process used. Thus gum rubber articles vulcanized from such plastic materials have much lower strength than have similar articles made from polymers which have not been so radically plasticized and masticatedp- An object of the present invention is to provide rubber-like compounds and a method of making the same, which compounds are capable of being compounded with curing agents and: cured to a state resembling vulcanized rubber, can be masticated and extrudedthrough a die to retain its shape, and may be cured in. open air or steam without requiring large amounts of inorganic filling materials, so that a resultant article maybe produced which is analogous to thosecomposed of soft vulcanized natural gum rubber and which is less deteriorated by masticating processes than are rubbers generally.

Other objects will be apparent from the following'description of the invention. r

This invention is largely possible because of, the small particle size of synthetic rubber particles in synthetic rubber latices, which syntheticparticles in contradistinction to the particles in natural rubber latex approach in fineness, if they are not finer, than many reinforcing pigments. In accordance with thepresent invention, a vulcam'zed synthetic latex is admixed with a latex of an unvulcanized and plastic rubbery polymer,

which may be natural rubber or a syntheticpoly.-

Since the vulcanized particles are cross-linked by sulfur or vulcanizing agent and are therefore extremely resistant to forces tending to cause their cross-linked by a rubber-vulcanizing agent,-such as sulfur, selenium, tellurium or any other rub.- ber-vulcanizing agent. A vulcanized synthetic latex or synthetic latex cross-linked by apolymer-vulcanizing agent is essential for forming the disperse phase of compounds of the present invention. The plastic particles that are formed into the matrix may be derived from anatural or synthetic latex, however.

Suitable latices for forming the vulcanized dispersephase of my compounds are the synthetic emulsion polymers of a liquid comprising a conjugated diolefinic compound such as but'adiene, isoprene, "chlo'roprene, 2,2-dimethylbutadiene and the like, preferably of six carbon atoms and less, and copolymers of one or more'of these conjugated dienes with a copolymerizable mono-olefinic compound, such as aryl-olefinic compounds having' the olefinic group in conjugated relation with an unsaturated linkage of the aromatic ring andincluding styrene, alpha-methylstyrene, 3,e-di chloro-alpha-methylstyrene and the like, the esters and nitriles of acrylic and methacrylic acids, vinyl pyridine, dimethylvinylethinyl, carbinol, methylisopropenyl ketone, etc. The plastic laticesto be mixed with the vulcanized latex include any one or more of those prepared from the above combination of monomers suitable for forming the disperse phase when vulcanized, and natural rubber as well. In fact, natural latex is especially desirable for the plastic matrix or continuous phase of my compounds, although the fine particle size of the vulcanized synthetic latex is required for the disperse phase. I

The particle size of synthetic latices as used for the disperse phase is extremely small, being but a fraction of that of natural latex and being generally less than 200 angstroms (A) in diameter. Some syntheticlatices, however, have particle sizes as low as 400 or 500 A. units, and they may run as high as 3000 or 4000, or even 5000 A. units when prepared by special procedures. Particles of the large particle size synthetic latices are but a fraction of the size of particles in natural rubber latex.

The polymerization of themonomeric' materials in forming the synthetic latices may be accomplished by any method and forms no part of the present invention. Generally, the monomeric materials are agitated in an aqueous. solution of an emulsifying agent, such as a fatty acid or rosin soapor other cationic or emulsifying agent, in the presence of a suitable free radical forming catalyst, such for example as a water-soluble or monomer-soluble per salt, such as benzoyl peroxide, hydrogen peroxide, potassium persulfate, etc;

Thecuring of the synthetic latex for the disperse phase may be accomplished by any suitable means that does not cause coagulation there-.

of, and processes used for making natural cured rubber latex are suitable. Generally, the preferred procedure is to incorporate into the syn- 4 thetic latex to be cured so that it forms the disperse phase of the compounds of the present invention an aqueous dispersion of a suitable curing agent, such as sulfur, and an aqueous dispersion 5 or solution of an organic accelerator, together with a suitable stabilizing agent, such for example as the Daxad, a condensation product of naphthalene sulfonic acid with formaldehyde, and/or other suitable protective colloid, if required, to prevent coagulation during the curing step. If an ultra accelerator is used the curing may be accomplished by allowing the latex mixture to stand at-room temperature. Generally it is incorporated into a closed container, preferably under gas pressure, and heated and stirred for sufiicient time to cause the particles of the dispersdpolymer to change from the plastic to the substantially elastic state. These particles, which are cross-linked by curing agents such as sulfur,

are extremely resistant to deformation; because of their extremely smalrparticle size,'correspo nding to or approaching reinforcing pigmentsthey. apparently are able to act as stiffeners orreim' forcing agents for the plastic component of the compositions of the present invention. They still retain their soft, resilient rubberlike'charac ter, however, and thus permit the retainmentof a soft rubber compound asdistinguishedfrom inorganic fillers and pigments heretofore used.

Because they are elastic and therefore more rigid than the plastic particles, these vulcanized pare ticles move bodily without appreciable injury in, the plastic matrix upon milling. and mastication ,g of the Wet or dried coagulum. The dispersed particles are therefore 'unmasticated and have their original unmasticated structure evenafter mastication of the coagulum or dry compound. The higher gum strength of the unma-s'ticated particles forming thedisperse is thus preserved 40 and deterioration of mastication is substantially The highergum entirely in the plastic matrix. M strength of the fine unmasticated particlesis thus able to act as a pigment to improve gum strength latices with one or more negative latices. This is especially true when the vulcanized and un vulcanizedlatices are in substantially equal proportions.

The proportions of the-two latices may be varied quite widely. As little of the vulcanized rubbery I solids (solids from the vulcanized rubber'latex);

as 10% by weight ofthe total polymer orru-bbery solids in the compound givesnoticeable improve,"-

ment in the resultant coagulum. But it is gen erally preferable that the'solids of the. vulcanized iicient' amount to maintain a continuous phase in the masticated ccagulum, and about 10% to 15% of the coagulum is usually requiredfor this purpose. The. stiffness of the unvulcanized com pounds or resistance to plastic flow is .substantially increased by increase in. the proportion of. the vulcanized phase when present in high pro-r portions, although extrudability is increased.

5. Around equal parts of disperse phase and matrix composition are desirable for most applications in that the compound, when sufficiently masticated, is readily extrudable and has sufiicient rigidity to permit curing of the extruded article in open steam without appreciable plastic flow.

The following examples, in which partsare by weight, illustrate the present invention:

Example 1 100 parts of a mixture of monomers containing 75 parts of butadiene, parts of dichlorostyrene and parts of styrene, having dissolved therein about .05 part of dodecyl ,mercaptan, are emulsified by agitation with 250 parts of water and about 5 parts of an emulsifying agent, such as soap, sodium oleate or polymethyl acrylamide, .25 part of sodium silicate and about .3 part of potassium cobaltinitrite. The emulsion thus obtained is incorporated into a vessel of such volume that it is completely filled with liquid. It is thereby polymerized by maintaining it with constant agitation at sli htly elevated temperatures of above 50 C. until there is obtained a latex having a total solid content of at least 65% or 70% of the theoretical possibility. Hydroquinone or other material capable of preventing further polymerization may if desired be added as is customary practice.., r

Into 100 parts of the latex thus obtained (based on the rubbery content thereof) is incorporated about 1 part of sulfur, 1 part of accelerator (piperidine pentamethylene dithiocarbamate) and a very small amount of zinc oxide, all in the form of an aqueous dispersion which contains a suitable amount of a wetting agent, such as sodium lauryl sulfonate, and about 3 parts of Daxad (a condensation product of naphthalene sulfonic acid and formaldehyde) or other suitable dispersin or stabilizing agent.

The compounded latex thus produced is, without coagulation, partially vulcanized in suitable manner, as by heating at about 160 F. in a closed vessel for about one and one-half hours.

Example 2 Parts solids Vulcanized standard GR-S latex (GR-S is a butadiene-styrene copolymer E of Reconstruction Finance Corporation) 109 Natural rubber latex 100 The above latices are mixed together, and the mixture coagulated by addition of salt and sulfuric acid. The coagulum is washed and dried and is compounded on a rubber mill in conventional manner with the usual curing agents, accelerator, zinc oxide and antioxidant.

The mastication on a rubber mill is continued until the mixture has a plasticity of about .0 units or less on a Mooney shearing disc plastometer. It is then extruded through a die to form a gasket and cured in open steam. The resultant product retains the general shape of the die, much better than does a homogeneous product of the same extrudability. The product also has the appearance of a soft gum rubber and has high tensile strength.

Example 3 Parts solids Vulcanized latex of Example 1 60 Standard GR-S latex 40 The above latices are blended, compounded in latex form with an aqueous dispersion of 1 part sulfur, 1 part accelerator and 1 part zinc oxide, and the mixture coagulated as in Example 2 with parts of 1 -33 (a thermatonic carbon black) 1 and i 6 f salt and sulfuricacid. The coagulum is washed, dried, masticated; and optionally mixed'with 10 25 parts of crude rubber. The mixture thus obtained is extruded through a die and" cured .in, open steam to form a rubber article. The re.-. sultant article is soft rubber-like and fiexibleand retains, after extrusion and curing, substantially the cross sectional shape of the extrusion die; ,1

In place of the ,GR-S. latex in Example 1, tone may use othercured synthetic latices. such as an aqueous dispersion of the copolymer of butadiene,

and acrylonitrile, or an aqueous dispersion of polymer formed from monomers containing other.

conjugated dienes as before mentioned in place of butadiene 1,3. The latex of Example, Lmay also be substituted in Examples 2 and 3 by ia"p.lurality of vulcanized or sulfur-cross-linked synthetic latices prepared from 'diiferentcomonm mers, and/or the same comcnomers in different proportions. The natural latex of Examplezrm'ay be substituted in whole or in .part byone or more unvuloanized, relatively. plastic synthetic latices or aqueous dispersions of plastic synthetic rubbery, polymers to give similar results. It 'is generally preferred for most purposes that the mixed latices.- Thus, vulcanized:

be compatible with each other. latices of, polymers soluble in aliphatic solvents,

as in Buna-S rubber and the like are'generally preferred with plastic natural rubber or plastic Buna-S latices.

by combining a vulcanized latex of a polymer soluble in aliphatic hydrocarbons with a latex of a plastic oil-resistant polymer, such as butadieneacrylonitrile copolymer obtainable under such trade names as Hycar OR-25 latex or Perbunan latex.

A vulcanized synthetic latex is one having particles of polymer cross-linked with a suitable vulcanizing agent, such as sulfur, so that the particles are in a more elastic state. It is thus distinguished from a latex having particles cross-linked by polymerization as described in my aforementioned application.

While sulfur has been used as the vulcanizing agent in the above examples, any of the various vulcanizing agents suitable for vulcanizing the respective polymer and forming a bridge between molecules of the polymer after polymerization may be used in place of all or part of the sulfur.

Although the invention may be employed in various ways, only preferred embodiments have been illustrated and described. Other embodiments may be made within the invention as provided by the patent statutes.

What I claim is:

1. A curable, dried mass of masticated coagulum from a latex comprising an aqueous dispersion of an unmasticated vulcanized copolymer of butadiene and styrene and an aqueous dispersion of a plastic polymer of a conjugated diolefinic compound of less than six aliphatic carbon atoms, said coagulum having a curing agent dispersed therein and having a plasticity of no more than 40 when measured under standard conditions on a Mooney plastometer, whereby it may be shaped and cured in shaped form.

2. The productofclaim 1 wherein the polymer oi the plastic *diolefinic compound is natural rubber.

3. In: a methodof making-a heterogeneous compound which'may be readily extruded to a shape through an extrusion die, :the steps which comprise forminga mixture of a vulcanized synthetic latex having-as -a disperse phase thereof .a-synthetic polymer 0f a diolefinic compound having not in excessof six aliphatic carbon atoms; and of a latex havingas a disperse phase thereofan vunmasticated unvulcanized plastic rubbery polymer of adiolefinic compoundhaving not in excess of-six aliphatic carbon atoms, coagulating the mixture thus formed, drying and .masticating compounding agents into the dried-coagulum.

4. The methodof claim 3 wherein the vulcanized synthetic latexisv an aqueous dispersion .of a copolymer of abutadiene and anarylvinyl compound.

:5. The method-of claimfi :wherein the vulcanized :syntheticlatexis an aqueous dispersion ofa copolymer of Ibutadiene and anarylv'inylcompound, and is characterized byhaving a particle size less than3000 .angstrom units, .and wherein the .plastic .latex is -an aqueous. dispersion of natural rubber.

v6. The method of. claim .3 wherein said masticatedtcoagulum extruded to a desired shape and cured.

.7. .An extruded and vulcanized article comprising .:a :;masticated, compounded, extruded, dried mass ofa-coagulum of amixture ofa vulcanized.

synthetic-.latexhaving. as a. dispersedzphasethereof a synthetic polymer ofa .diolefinic compound having not in excess of six. aliphatic carbon: atoms andof a latex'having as a dispersed phase'thereof a masticated unvulcanized plastic rubbery polymer of a diolefinic compound havingnotiin excess of six aliphatic carbonatoms. said c.oagu lum having a continuousphase of particles of said unvulcanized plastic polymer smeared together.

8. A molded article comprising a vulcanized shaped mass 'of -a masticated and compounded dried coagulum of-a-mixture ofa vulcanizedsynthetic latex having as a dispersed phase thereof a synthetic polymer of a ldiolefinic compoundhaw ing not in excess=of six aliphatic-carbon atoms and of alatex having as a dispersed phase thereof a masticated unvulcanized plastic rubbery polymer of a diolefinic compound having notinexcess of six aliphatic carbon atoms.

THEODORE A. TE .GROTENHUIS.

REFERENCES CITED The following references are of record 'in-the file of this patent:

UNITED STATES PATENTS Number Name Date 1,831,895 Van Arsdel et-al. Nov. 17, 1935 1088 407 Dales et al. .July-'27,'1937 2,335,104 'Britt et-al Nov. .23, 1943 

1. A CURABLE, DRIED MASS OF MASTICATED COAGULUM FROM A LATEX COMPRISING AN AQUEOUS DISPERSION OF AN UNMASTICATED VULCANIZED COPOLYMER OF BUTADIENE AND STYRENE AND AN AQUEOUS DISPERSION OF A PLASTIC POLYMER OF A CONJUGATED DIOLEFINIC COMPOUND OF LESS THAN SIX ALIPHATIC CARBON ATOMS, SAID COAGULUM HAVING A CURING AGENT DISPERSED THEREIN AND HAVING A PLASTICITY OF NO MORE THAN 40 WHEN MEASURED UNDER STANDARD CONDITIONS ON A MOONEY PLASTOMETER, WHEREBY IT MAY BE SHAPED AND CURED IN SHAPED FORM. 